Ahhh... those new year's resolutions to get back the buff bod that you had 5, 10, 20 years ago, can be pretty motivating in terms of getting off your chuff, and into a high-calorie-burn spin class! Often, though, important safety issues can be overlooked - such as taking into consideration what may be lurking around the shower floors (bacteria, germs, fungus, etc), or on the gym equipment.
When I go to the gym, I take antibacterial wipes so that I can wipe down any suspect areas - and for the shower, I always wear flip-flops. Of course some gyms are cleaner than others, which you have likely found if you have been shopping around - and this aspect always weighs heavily in my decision as to whether or not to sign a membership agreement with any given gym.
One time, I wanted to sign up with a gym, and I asked for a day-pass so I could try it out (always do this - do not undervalue a free trial, your health isn't worth the risk of signing a membership agreement relatively blindly/on good faith), and I decided to work with one of their personal trainers on cardio boxing. The trainer suggested/insisted I wear gloves, but when I put them on - I noticed that they felt grimy, and soon after I noticed a terrible odor - which I realized was coming from the gloves. I immediately took the gloves off, but the smell was still on my hands, and I had to go immediately and wash them several times. Yes, you could take your own gloves - but the fact that those gloves were being provided for guests/members to use, was a little discouraging.
Another issue that needs to be addressed is wearing the correct shoes for the work-out you are doing - e.g. you need different support for running on the gym's track than you would using the treadmill - talk to one of the trainers' at the gym to make sure you have the right support for the work-out/s you plan to undertake.
Be sure to keep yourself hydrated - and do your research on those energy drinks, if that's what you plan to have with you at the gym - some of them are just marketing gimmicks, and at the end of the day you are responsible for everything you put into your body - make sure it's not mostly "high-fructose corn syrup", go for a natural drink with healthy ingredients that will assist you in your goal to look and feel your best.
Be sure to inform someone at the gym if you have any health-related concerns - especially if you are using a gym that is not your regular location - and give them your doctor's contact information in case anything should happen while you are there (this should be listed in your membership profile - however, most gym employees are young and could potentially be overwhelmed by a medical emergency - and if you are just trying out the gym, or have a temporary trial, they may not automatically have your medical information available if anything went wrong) - this will give you some added peace-of-mind knowing that someone's looking out for you.
Avoid adopting the no-pain-no-gain mentality - yes, you should likely feel a burn - but talk to a trainer if you experience any pain - you may be using a machine/piece of equipment incorrectly, they can guide you in terms of how many repetitions/what kind of equipment, or exercise, to do.
And most of all, be sure to leave any negativity at the door - in order to do well, and get into great shape, a positive attitude is a must - otherwise, the sight of Barbie or Ken could likely deliver a blow to your enthusiasm!